Pyrolysis gasoline is a byproduct C5-200° C. during the preparation of ethylene, the yield of which is above 50% to 80% of ethylene production capacity, wherein the amount of aromatics is more than 50%, making the pyrolysis gasoline an important source for aromatics. The pyrolysis gasoline also comprises highly unsaturated hydrocarbons such as diolefin, styrene and the like that are convertible to corresponding monoolefin via selective hydrogenation and act as the starting material for extracting aromatics. Recently, ethylene industry has been largely developed and the ethylene production capacity is improved yearly, leading to substantial increasing of the yield of pyrolysis gasoline that is an important byproduct of ethylene. The hydrogenation technique focusing on the hydrogenation catalyst of pyrolysis gasoline is an important branch in the field of hydrogenation and plays a critical role in the post-treatment of preparation of ethylene by steam cracking.
Currently in industry, the catalyst for the first stage selective hydrogenation of pyrolysis gasoline mainly comprises platinum and palladium catalysts, with the majority being palladium-based catalysts. Palladium-based catalysts are advantageous to have low start temperature, high hydrogenation activity, large feed capacity, long lifetime and so on. However, in part of the feed for hydrogenation apparatus of pyrolysis gasoline, the amount of water and arsenic is in excess, and the distillate is too heavy, and the hydrogenation load is too large, leading to the low stability and short lifetime of the current catalysts in industry process.
CN 200410061031 reports a palladium-alumina catalyst, and the preparation thereof. The application relates to using Al2O3 calcinated at elevated temperature and precoated with proper amount of alkaline earth metal oxide as a carrier, and impregnating the carrier with 0.15% to 0.24% of palladium to produce the catalyst. CN 1175931C reports supported palladium-alumina catalysts for hydrogen peroxide production by anthraquinone route and the preparation thereof. The application relates to using Al2O3 calcinated at 900 to 1000° C. and precoated with proper amount of rare earth oxide as a carrier, and impregnating the carrier with 0.15% to 0.25% of palladium to produce the catalyst. CN 85100761A discloses a fiber carrier catalyst for selective hydrogenation of diolefin which is the distillate of pyrolysis gasoline, characterized in the use of η-Al2O3 porous fibrous carrier having a specific surface area of 20 to 150 m2/g and a pore volume of 0.1 to 0.3 ml/g. The catalyst has a high initial activity, but the pore volume is too small. When the content of colloid, water and arsenic in the feed for pyrolysis gasoline hydrogenation apparatus is in excess, the pores on the catalyst are readily coked and blocked, which influences the hydrogenation stability of the catalyst.
An excellent selective hydrogenation catalyst should have high hydrogenation activity and good selectivity, and more importantly, it should have good stability. That is, the catalyst should be water-resistant and colloid-resistant, so as to extend the lifetime of the catalyst.